1. Field of the Invention
The present invention relates to power generation apparatuses used in electric power generators and the like.
2. Description of the Related Art
Recent years have, due to concerns for energy conservation, seen an increased need for electric power generators that collect so-called “waste heat” from various types of facilities such as factories and generate electricity using the energy from the collected waste heat.
The waste heat electric power generator disclosed in, for example, Japanese Patent No. 4557793 is known as such an electric power generator. This waste heat electric power generator includes a closed-loop circulating channel in which a working fluid evaporator, a turbine for causing the working fluid vapor to expand, a condenser for condensing the working fluid vapor, and pumps for circulating the working fluid are connected in series. Thermal cycling is carried out in the circulating channel when the working fluid is being cycled, while the stated turbine generates power and drives an electric generator using that power. Note that particularly among such waste heat electric power generators, binary generation systems, which use the Rankine cycle to drive turbines, expanders, or the like using a low boiling point working fluid, are well-known.
The stated waste heat electric power generator includes a steam generator that collects waste heat and generates high-pressure working medium vapor from the working medium, a turbine that expands the high-pressure working medium vapor, a condenser that condenses low-pressure vapor from the turbine, and a working medium circulating pump that circulates the working medium. These elements are connected by a working medium circulation channel, and a gas-liquid separator is disposed between the steam generator and the turbine. Working medium vapor that has been separated from the working medium liquid by the gas-liquid separator is introduced into the turbine.
Note that in the stated waste heat electric power generator, it is necessary to provide a circulating pump in order to circulate the working medium through the circulating channel, and liquefied working medium condensed by the condenser located upstream from the circulating pump is sucked into the circulating pump. The circulating pump serves to send the liquefied working medium to the steam generator located downstream.
It is necessary to take measures in order to preempt the occurrence of cavitation in the circulating pump. Cavitation is a phenomenon in which, in a fluid mechanism, the pressure of a medium (liquid) that flows within the fluid mechanism reaches the maximum vapor tension locally, causing the medium to boil and producing small bubbles. When these bubbles are burst, the impact pressure thereof causes what is known as erosion in the constituent components of the fluid mechanism. For example, if the fluid mechanism is a turbo fluid mechanism, the impeller, which is the primary component thereof, will be damaged. In the case where cavitation has occurred in a circulating pump, it is necessary to stop the operation of the entire electric power generator system in order to perform maintenance on the circulating pump. Therefore, it is important to take measures to preempt the occurrence of cavitation in the circulating pump.
In addition to the constituent elements described above, this waste heat electric power generator is provided with a circulation amount control means that controls the amount of the working medium that is to be circulated from the condenser to the steam generator, and a liquid surface detector that detects the surface of the liquid separated in the gas-liquid separator. The separated liquid (working medium) separated by the gas-liquid separator is introduced to the condenser via a flow amount control means, and the circulation amount control means controls the circulation amount of the working medium so that the separated liquid surface within the gas-liquid separator detected by the liquid surface detector reaches a predetermined level.
Furthermore, this waste heat electric power generator is provided with a heat collector. The heat collector is provided along the channel that leads the separated liquid from the gas-liquid separator to the condenser, and exchanges heat between the separated liquid and the working medium fed from the condenser to the steam generator.
Because no measures are taken in the stated waste heat electric power generator to preempt the occurrence of cavitation in the circulating pump, there is the risk that cavitation will occur in the circulating pump.
Note that to prevent the occurrence of cavitation, it is necessary for the channel on the upstream side of the circulating pump to be filled with the liquid-state working medium, and it is further desirable for the amount of the working medium in the liquid state that fills the channel on the upstream side to be greater than or equal to a desired predetermined amount. However, the aforementioned Japanese Patent No. 4557793 makes no particular mention of a method for stopping the waste heat electric power generator or, conversely, a method for starting the waste heat electric power generator. Accordingly, depending on the methods for stopping and starting the waste heat electric power generator, a situation in which the channel on the upstream side of the circulating pump is not filled with the working medium in a liquid state when the waste heat electric power generator is started, or a situation in which the amount of the working medium in a liquid state that fills the channel on the upstream side is less than the desired predetermined amount, will occur. This further increases the risk of cavitation occurring in the circulating pump.